Resistance switching devices, also called memrisitive devices, have attracted extensive interest for applications including non-volatile memory, reconfigurable switches, bio-inspired neuromorphic computing and radiofrequency switches. While typically fabricated from relatively simple metal/insulator/metal (MIM) structures, memristive devices have shown highly desirable properties including low power consumption, fast switching speed, and great cycling ability. To date, a wide variety of material systems have been developed for memristive devices that work under different mechanisms. For electrochemical metallization memory (ECM) systems, it has been observed that formation and dissolution of metallic filaments (e.g., copper—Cu or silver—Ag) are responsible for the low and high resistance states. On the other hand, for valence change memory (VCM) type of systems such as Pt/TiO2/Pt/Ti and Ta/TaOx/Pt, it is widely accepted that the motion of oxygen anions (or equivalently the positive-charged oxygen vacancies) leads to valence changes of the metal (cations) and hence the resistance changes of the metal oxide materials. These devices can also form a conduction channel between the two metal layers of the MIM structure. The conduction channel can be a newly formed conductive crystalline sub-oxide phase such as Ti4O7 in TiO2 based devices, or an amorphous metal-oxygen solid solution such as Ta(O) in TaOx systems. Recently, based on scanning tunneling microscopy (STM) studies it was proposed that the migration of cations, in addition to oxygen anions, could also contribute to the resistive switching behavior in typical VCM materials such as TaOx, TiOx and HfOx. However, direct visual observations of conduction channels induced by cations migration inside the switching oxides and a physical model concerning the roles of both cations and anions during the resistance switching in VCM-type devices have not been revealed prior to the work described herein.